1. Field of the Invention
The present invention relates to a double capsule for cosmetics and to a cosmetic composition containing it. More particularly, the present invention relates to a double capsule for cosmetics obtained by a matrix-double encapsulation method which comprises steps of (a) first-encapsulating fat-soluble active materials with filming materials to give a microcapsule; and (b) matrix-encapsulating the microcapsule of the step (a) with gellan gums. The present invention can improve the stability of the fat-soluble active materials in the cosmetic base and feel of the cosmetics.
2. Related Arts
The fat-soluble materials are widely used as an active ingredient in cosmetics. The representative examples include retinoids such as retinols, retinoic acids, retinaldehydes and their derivatives; tocopherols; unsaturated fatty acids and their derivatives, fat-soluble pigments, and vitamin F. But they are easily oxidized in air or in aqueous solution, and lose their stability. Especially, although retinol has an outstanding effect in preventing the formation of wrinkles, it has a limit in the use as a cosmetic material due to its instability.
So, in order to incorporate retinol into the cosmetic formulations, it has been used in the form of a water in oil type (W/O type) emulsion. However, in this case, the W/O type emulsion containing retinols tends to be oily and greasy. Additionally, it is unsatisfactory in its stability.
Under this circumstance, many studies have been conducted to provide a method for stabilizing the fat-soluble active materials in cosmetic formulations. For example, the encapsulation method has been introduced in order to stabilize the fat-soluble active materials in the cosmetic formulations.
Usually, the encapsulation techniques for cosmetic materials are divided into the common encapsulation and the matrix encapsulation. In the common encapsulation, active materials as a content are surrounded with filming materials as an outer film. On the other hand, in the matrix encapsulation, active materials are mingled with the filming materials in the series. These encapsulation techniques make it possible to insulate the active materials which have bad compatibility with the cosmetic base within the filming materials, so that their stability in the cosmetics can be improved. Further, the encapsulated active materials can be protected from the outside unfavorable factors and can keep their physicochemical properties until they are applied to the skin. In addition, there is an advantage of ease in handing liquid active materials by encapsulating them. And, there is another advantage of diversifying the function or the effect of the active materials by regulating the particle size and the release speed of the capsule contents.
However, in the common encapsulation techniques, since the filming material is water-soluble and easily swollen in water, water in the cosmetic base may easily penetrate into the capsule or the active ingredient in the capsule may be released. And, when the film of the capsule is hardened or thickened, residues of the film remains onto the skin due to poor pressure-collapse resulting in a poor feel of cosmetic formulations or causing irritation to the skin. Further, in the matrix encapsulation techniques, the active ingredient may be released through the capillaries of the capsule particle.
Under these circumstances, the present inventors have conducted extensive studies in order to provide a new encapsulation technique that allows stabilizing the fat-soluble active material in a cosmetic base without any problems such as soaking water into the capsule, releasing the capsule content into the cosmetic base, or poor feel of cosmetic formulations. As a result, we found that this object can be accomplished by a matrix-double-encapsulation technique.